Retrieved From; http://www.smogtips­.com/frequentlyasked­questions.cfm>

Depending on the year make and model of vehicle you own, this system is>different. If you own a 1996 or newer vehicle you more then likely own>a vehicle which is equipped with an On-Board Diagnostics system called>OBD II, as opposed to an OBD I system which older vehicles were>equipped with. The OBD II Diagnostic system is designed to monitor all>aspects of your engine's emission conditions and report this>information to a central database within it's computer. This>information is processed and checked against the computers>pre-deter­mined values for various inputs levels and performance>pattern­s. If any problems are found, the computer will determine>whether to alert the driver or not. If a decision has been made to>alert the driver of an emissions problem, the "Check Engine" or "Engine>Malfunction­" light will illuminate on the vehicle's dashboard. In more>serious emission conditions the computer may even begin to rapidly>flash the "Check Engine/Malfunction"­ light indicating to the driver,>that the vehicle needs immediate diagnosis/repair attention.>

Now here's what the smog test has to do with the OBD II system...Your>vehic­le is equipped with an OBD II computer AND a link to connect the>OBD II computer to a Smog Check Analyzer or Data Scan Tool (available>at most auto part stores). The OBD II link relays all "Check Engine">conditions along with stored Trouble Codes with in the center database,>to the smog machine during the time of the smog inspection. If any>codes are present which cause the Check Engine light to illuminate>either regularly or intermittently, the vehicle fails the smog>inspection. Here's the tricky part, not all computer codes illuminate>the Check Engine light.>

In fact I can say there are two types of codes, bad codes and good>codes. The good codes are the "Readiness Flags". These Readiness Flags>indicate that certain emissions systems which the OBD II computer has>been monitoring have PASSED the test, indicating that those systems are>working properly. Then there are the bad codes. The bad codes are>actual "Trouble Code". These codes indicate that the OBD II computer>has detected a problem with in the emissions system. The Trouble Code>will specifically indicate the component and problem which was found.>Newer vehicle's have very complex codes in the thousands.>

A vehicle will fail the smog inspection if the proper "Readiness Flags">are not set. A vehicle will also fail the smog inspection if any>"Trouble Codes" are present. So it is possible for a vehicle to fail>the smog inspection without the "Check Engine" light on. "Readiness>Flags" do not cause the "Check Engine" light to illuminate, but may>cause a vehicle to fail the smog test.>

Now here's the fix... in order to set all the proper "Readiness Flags">the OBDII system must complete at least one drive cycle (in some cases>two or three). A drive cycle is a sequence of internal tests which the>OBDII computer runs while your vehicle is being driven. This insures>all emissions systems are functioning properly. Only then will your>vehicle pass the smog inspection. A drive cycle usually requires one>week of driving.>

I hope this information is helpful to you. If there is anything I can>help with in the future, don't hesitate to e-mail.>

For more information you may want to locate a reputable smog service>center in your area by simply typing in your zip code in the Smog Shop>Locator search section at www.smogtips.com>

Sincerely,>Alec - SmogTips Support http://www.smogtips­.com>

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